1. Field of the Invention
The present invention pertains to a fuel mixture enrichment system particularly adapted for starting manually cranked two stroke cycle internal combustion engines wherein a predetermined quantity of liquid fuel is injected into the engine intake air flow stream during engine starting.
2. Background
In the art of internal combustion engines of the type wherein fuel is premixed with engine intake air in a carburetor or throttle body various systems have been developed for enriching the fuel-air mixture to enable the engine to start and run during a warm-up period. The conventional method of enriching the fuel-air mixture in both four stroke cycle and two stroke cycle engines includes a choke or secondary throttling valve which is held substantially closed during engine starting to restrict air flow and promote increased liquid fuel flow into the engine inlet air flow stream to provide a relatively rich fuel-air mixture.
However, conventional air flow throttling choke mechanisms as well as other known types of priming or mixture enriching devices have certain disadvantages and do not function well with carburetors for lightweight two stroke cycle type engines, particularly carburetors of the type that are adapted for use in a variety of engine directional attitudes. Small two stroke cycle engines are widely used on hand held power tools used by persons generally unfamiliar with internal combustion engine manual starting techniques. These engines are adapted for use in a variety of directional attitudes and they typically utilize a carburetor of the so called diaphragm type wherein a relatively small reservoir of fuel is maintained in the carburetor body for metering through the idle and high speed orifices or jets. The lack of fuel in the carburetor of the type of engine described above after a period of disuse makes these engines particularly difficult to start utilizing conventional air throttling type choke mechanisms. On the other hand starting of most two and four stroke cycle engines utilizing conventional choke devices can also be difficult in respect to the fact that if the choke is left closed through too many cranking cycles without an engine start, the engine may become flooded and continue to flood to a point where starting is hopeless until the engine has been left idle long enough to allow the excess fuel in the crankcase and/or the combustion chamber to evaporate and a proper fuel-air mixture to be restored. Manually operated chokes are also cumbersome to operate for inexperienced persons and must be constantly and quickly adjusted once an engine start is achieved to prevent flooding and thereby stalling the engine.
Although certain types of mixture enriching or priming systems other than chokes have been developed for carbureted engines and other types of engines having fuel-air mixing before introduction into the combustion chamber, known systems have not been successful for a variety of reasons. One problem associated with known types of priming systems pertains to the lack of mechanism for injecting consistently precise measured quantities of fuel to avoid flooding the engine. Accordingly, the number of priming strokes during engine start and warm-up operation cannot be easily determined or controlled. Moreover, known systems are generally adapted for use with engines having float bowl type carburetors as opposed to engines with diaphragm type carburetors or fuel injection systems. Another disadvantage of known types of priming systems used in conjunction with conventional downdraft or sidedraft carburetors is that, if the engine fails to start after one or two starting cycles, the mixture present in the engine intake system and combustion chamber usually becomes richer, if priming is continued, to the point of flooding the engine.
Yet another starting problem occurs when an engine has run out of fuel and wherein the engine must be cranked through several starting cycles just to pump fuel from the engine fuel tank to the carburetor. This problem is particularly acute with small engines with so called diaphragm type carburetors or with priming systems, including chokes, which rely on fuel at the carburetor to provide the rich mixture required for starting. All of the abovementioned engine starting problems are, of course, aggravated when the engine is in the hands of an inexperienced user. However, the problems associated with prior art types of fuel priming systems have been overcome with the mixture enriching system of the present invention.